Concurrent posttraumatic stress disorder (PTSD) and traumatic brain injury (TBI) is common in military populations. The purpose of this study was to examine long‐term neurobehavioral outcomes in service members and veterans (SMVs) with versus without PTSD symptoms following TBI of all severities. Participants were 536 SMVs prospectively enrolled from three military medical treatment facilities who were recruited into three experimental groups: TBI, injured controls (IC), and noninjured controls (NIC). Participants completed the PTSD Checklist, Neurobehavioral Symptom Inventory, and the TBI–Quality of Life (TBI‐QOL) and were divided into six subgroups based on the three experimental categories, two PTSD categories (i.e., present vs. absent), and two broad TBI severity categories (unMTBI, which included uncomplicated mild TBI; and smcTBI, which included severe TBI, moderate TBI, and complicated mild TBI): (a) NIC/PTSD‐absent, (b) IC/PTSD‐absent, (c) unMTBI/PTSD‐absent, (d) unMTBI/PTSD‐present, (e) smcTBI/PTSD‐absent, and (f) smcTBI/PTSD‐present. There were significant main effects across the six groups for all TBI‐QOL measures, ps < .001. Select pairwise comparisons revealed significantly lower scores, p < .001, on all TBI‐QOL measures in the PTSD‐present groups when compared to the PTSD‐absent groups within the same TBI severity classification, ds = 0.90–2.11. In contrast, when controlling for PTSD, there were no significant differences among the TBI severity groups for any TBI‐QOL measures. These results provide support for the strong influence of PTSD but not TBI severity on neurobehavioral outcomes following TBI. Concurrent PTSD and TBI of all severities should be considered a risk factor for poor long‐term neurobehavioral outcomes that require ongoing monitoring.